German Published Patent Specification 2,651,639, (U.S. Patent application Ser. No. 845,174), claims a process for the preparation of carbonic acid aryl esters of polyester-polyols from polyester-polyols with an average molecular weight (Mn) above about 250, preferably above about 600, and carbonic acid bis-aryl esters, comprising heating the polyester-polyols with the carbonic acid bis-aryl esters at temperatures between about 100.degree. C. and 200.degree. C., in vacuo below about 35 mm Hg in the presence of catalysts, more than one mol of carbonic acid bis-aryl ester being employed per OH group, and distilling off the hydroxyaryl compound formed and the excess carbonic acid bis-aryl ester.
Suitable polyester-polyols are, in particular, reaction products of polyhydric, preferably dihydric and optionally also trihydric, alcohols with polybasic, preferably dibasic, carboxylic acids.